I started a forum on this a while back. If you look at my projects it is included as Iron Buff. It will stain your walnut BLACK. Here it is: 1. Take a pad of steel wool & rinse it with lacquer thinner to remove the protective oil coating. Tear it into pieces.2. Get a 1 pint glass jar and punch 2 holes in the lid with a nail. This will keep it from exploding. 3. Fill the jar with white vinegar and add the steel wool pieces. Let it sit for 7-10 days. The acid in the vinegar will dissolve the steel wool.4. Strain the liquid through an old t-shirt and again through a coffee filter.5. Brush it on your piece as you would any stain. This is a chemical reaction, however, and not a stain, so your finish will always be consistent, with no darker areas or brush marks. It will leave you with a darkly stained piece with a slightly raised grain, so don’t apply this till just before your final sanding, or you will sand through the stain. On walnut, however, you may not notice it.6. Every batch of this will turn out a little different, so in staining a large piece like a desk, increase the proportions, i.e. 1 pad steel / 1 pint white vinegar to as much as you need so you get consistent staining across the piece.

I hope you try this method on your project at hand. It is not as much trouble as it sounds and delivers great results. Woodworkers used this method for centuries before they discovered MinWax & etc. It will take any additional stain or varnish no problem. Another thing, it smells like pickles till you varnish it.